Question 1077273

Hi can someone help me with this problem please? THANK YOU! 

   Find the exact value of cos(2 theta)

          cos(theta)=-15/17 and theta terminates in QII.

         a.-240/289
         b.161/289
         c.120/289
         d.16/17
<pre>{{{cos (2theta) = 2 cos^2 (theta) - 1}}}
{{{cos (2theta) = 2 (- 15/17) - 1}}} ------ Substituting {{{matrix(1,3, (- 15)/17, for, cos^2 (theta))}}}
{{{cos (2theta) = 2(225/289) - 1}}}
{{{cos (2theta) = 450/289 - 1}}}
{{{highlight_green(matrix(1,7, cos (2theta), "=", 450/289 - 289/289, "=", 161/289, "(CHOICE", "b.)"))}}}